On this page you will a find a short guide on how to set up this bluetooth adaptor under Linux and how to connect your Siemens S55 mobile phone.
You might think 'Oh, yet another bluetooth howto'. Well, when I searched the web I found only questions concerning these devices, but no answers whatsoever.

Step 1: Kernel-Config

The necessary Parameters in the kernel-.config-file are
CONFIG_BLUEZ=m
CONFIG_BLUEZ_L2CAP=m
CONFIG_BLUEZ_SCO=m
CONFIG_BLUEZ_RFCOMM=m
CONFIG_BLUEZ_RFCOMM_TTY=y
CONFIG_BLUEZ_HCIUSB=m

Step 2: Install Necessary Software

Install the following software packages:

for debian users:
add the following line to /etc/apt/sources.list:
for testing:deb http://bluez.sourceforge.net/download/debian/ ./
for woody:deb http://bluez.sourceforge.net/download/debian/woody/ ./
run: apt-get update

Step 5: Connect S55

Start Bluetooth on your S55
Menu: 9-6-4

In the same submenu set 'visible to others' to 'always visible'.
Don't forget to switch back to 'Not visible' after finishing the setup.

Scan for the phone to get the hardware address. You could also get it from the
bluetooth-submenu on the phone, but this is also a first test of the connection
between computer and mobile.
On the right you see 'My BT Name' which you can configure on the phone.

$ hcitool scan
Scanning ...
00:01:E3:6F:7E:47 You got me
$

You can ping the phone to test the connection:

$ l2ping 00:01:E3:6F:7E:47

Add the following lines to your /etc/bluetooth/rfcomm.conf:

rfcomm0 {
bind yes;
# Bluetooth address of the device
device 00:01:E3:6F:7E:47;
# RFCOMM channel for the connection
channel 0;
# Description of the connection
# IMPORTANT: comment must be the same as BT name of the phone
comment "You got me";
}

In order to use the phone as a regular modem you need to bind
/dev/rfcomm0 to the hardware-address of the phone.

$ rfcomm connect rfcomm0 00:01:E3:6F:7E:47

When connecting the two devices for the first time you might be asked to enter a
PIN-Code on the phone. Enter some numbers and press 'Okay'rfcomm will ask you to enter the PIN-Code for the mobile
phone.
Enter the same numbers and press <Enter>/Click Okay.
Both devices will now connect to each other.

Success!!
Now you can use /dev/rfcomm0 just like a serial device to connect
to the BT-device.

Important:

When and if asking for the PIN-Code rfcomm will open a X-window.
This means that the User you run rfcomm as needs to be able to
access your X-Display (via ssh and X-forwarding or the $DISPLAY-Variable and
MIT-COOKIES).

Important 2:

When using one BT-Dongle on several computers don't forget to delete the
known-device-name of one computer when connecting to another, else the mobile
phone won't connect.

Now you can use the mobile phone like a regular modem via
/dev/rfcomm0. Fire up any terminal program like
minicom to test and play.

Before closing the connection by switching off bluetooth on the mobile phone it
might be advisable to run rfcomm release all (though I don't know
what would happen if you did not).